1. Field of the Invention
The present invention relates to a printed circuit board and a method of manufacturing the same, and, more particularly, to a high density printed circuit board and a method of manufacturing the same which enable a thin printed circuit board to be manufactured and can overcome problems occurring in a conventional method of manufacturing a printed circuit board because a conventional copper clad laminate (CCL) is not used as a raw material. The present invention relates to a printed circuit board.
2. Description of the Related Art
With the development of the electronic industry, electronic parts having high functionality and small size have been required. In particular, the demand for decreasing the thickness of electronic parts which are installed in portable terminals, in order to decrease the thickness of the portable terminals, is increasing.
In this situation, the reduction of the height of a package is one of the principal issues.
As various services in the mobile communication field are increasing, the number of electronic parts which are installed in a mobile phone is also increasing. Since the reduction of the area of the mobile phone is one of the demands of the final user, the trend that several chips are mounted on one interposer is increasing.
A Chip Scale Package (CSP), which is used as an interposer for ICs, has been widely used in mobile phones. Recently, almost all packages are using CSP, and almost all lCs are being stacked in such a CSP.
However, in order to stack more ICs, since the total height of the package is constant, methods of mounting the ICs while maintaining the height of the package have been sought in two directions.
That is, the methods include a method of decreasing the thickness of the ICs and a method of decreasing the thickness of the interposer.
The thickness of ICs ranges from 50 μm to 75 μm, and high level techniques for mounting them have already been established. Although researches into ICs thinner than the thickness range are being conducted, it is considered that such techniques have reached the limit of current technology.
The interposer is also becoming extremely thin, but it is considered that the techniques for decreasing the thickness of the interposer have also reached limit of current technology. Accordingly, in order to further decrease the thickness of the interposer, the technique for decreasing the thickness of components of the interposer by approaching the lower limit values of the components has been studied.
Meanwhile, in a conventional process of manufacturing a printed circuit board, methods of forming a circuit are classified into a tenting method (an etching method) and an additive method.
The tenting method is a method of forming a circuit pattern by forming an etching resist pattern on a copper foil formed on a CCL to a constant thickness, and etching portions other than the circuit by dipping a substrate, on which the etching resist pattern is formed, into an etching solution.
The additive method, which has recently been widely used, is a method of realizing a circuit pattern by forming a plating resist pattern on a CCL, plating only portions to form a circuit, and removing the plating resist pattern.
The tenting method has a low manufacturing cost, but has a limitation in forming fine circuit patterns. Accordingly, to overcome that limitation, the additive method is employed.
FIGS. 1A to 1D show a conventional method of manufacturing a printed circuit board using a semi-additive method.
In FIG. 1A, a plating resist pattern is formed by applying a plating resist 13 on the surface of the copper foil 12 of a CCL, which includes the copper foil 12 and a reinforced substrate 11, and developing the plating resist 13.
The thickness of the copper foil 12 of a typical CCL is about 0.5 μm to 3 μm. Typically, a photosensitive dry film is used as the plating resist 13.
In FIG. 1B, a plating layer 14 is formed through electrolytic plating. During plating, the copper foil 12 serves as a seed layer. However, in this case, the thickness of the plating layer 14 formed through electrolytic plating is not constant throughout the entire region due to deviation occurring during plating.
In FIG. 1C, the remaining plating resist 13 is separated after the plating is completed.
When the plating resist 13 is separated, it is removed by dipping the resulting CCL into a separating liquid. In this case, there is a problem in that the plating resist 13 is not completely removed, thus some of the plating resist 13 remains on the side walls of the plating layer 14.
In FIG. 1D, when the portions of the copper foil 12 that do not form a circuit pattern are removed through soft etching, and thus only a desired circuit pattern remains, the circuit pattern is formed.
However, even when the additive method is employed, it is still impossible to obtain a desired thickness.